Previous studies have evaluated medication errors (MEs) and adverse drug events (ADEs) in broad patient settings. The inpatient psychiatric population is a unique population whose risks for MEs, however, are less well known. Inpatient psychiatric pharmacotherapy may be associated with different rates and types of serious MEs because of differences associated with psychiatric patients, psychopharmacologic agents, and the psychiatric inpatient setting. Some data suggest that ADEs due to psychotropic medications may be more responsive to prevention efforts than other drug classes. We propose to study the epidemiology of serious MEs in hospitalized psychiatry patients and then apply these lessons in an interventional study. Serious medication errors include preventable ADEs and nonintercepted potential ADEs. Aim 1: To study the incidence and nature of serious MEs in hospitalized psychiatric patients. Aim 2: To design a multimodal intervention to prevent serious MEs in this patient population. Strategies will incorporate previous successfully demonstrated approaches, including those developed by our group (e.g., information technologies) and knowledge learned earlier during the study for aim 1. Aim 3: To conduct a randomized control trial of the effectiveness of an intervention to prevent serious MEs in psychiatric inpatients. This prospective cohort study will be conducted in three phases. In phase 1, we plan to identify the incidence, type, and preventability of serious MEs in psychiatric inpatients. During phase 2, we plan to incorporate knowledge learned in phase 1 in order to develop strategies to prevent serious MEs in the psychiatric inpatient setting. Finally, phase 3 will consist of a randomized control trial to study the efficacy of a practical multimodal serious ME prevention intervention. We will compare the intervention arm (serious ME prevention strategies) to both the control arm (no intervention) and to the baseline period (phase 1) in order to address secular trends that may occur in phase 3. We plan to conduct this study at McLean Hospital, a leader in the treatment of mental illness and chemical dependency. As a major teaching facility of Harvard Medical School, McLean Hospital maintains the largest program of research in neuroscience and psychiatry of any private psychiatric hospital in the United States.